Pre-moistened cleansing wipes are well known and are referred to as wet wipes, towelettes, and the like. They include a substrate, such as a nonwoven web, pre-moistened with a lotion, such as an aqueous lotion. Typically, pre-moistened wipes are provided as either folded, stacked, sheets or as a perforated roll which are meant to be used one at a time. There are two basic types of containers for providing sheets of pre-moistened wipes—a reach-in container or tub and a pop-up container. In a reach-in container the trailing edge of a wipe being extracted from the container is interwoven with the leading edge of the next wipe. This facilitates the removal of subsequent sheets form the tub. However in a pop-up container, the sheets are still in roll form. The roll is standing on end and is perforated for tearing off sheets. When the roll is pulled through an aperture or opening in the container, a sheet can be torn off at the perforations leaving a nub of the subsequent sheet protruding through the aperture. In order to be useful in pop-up containers, the wet strength of the wet wipes must be such that the integrity of the wipe is maintained; i.e., the wipe does not rip or tear as it is being removed from the container.
Historically, the level of self-crosslinking monomer in the dispersion has been increased in order to improve the properties of the wipes. However, the level of wet tensile typically plateaus at a performance level below what is now required and increasing the level of self-crosslinking monomer does not enhance performance. Rather it simply increases the viscosity of the dispersion, making it too thick for the standard means of applying the binder onto the web; i.e., by spraying. Until recently, the amount of performance obtained from traditional binders has been adequate for the majority of the needs as tub wipes dominated the market. However, new wipes have been introduced that are pre-moistened with cleaning or polishing lotions and are used, for example, to polish furniture or automobiles. Many are used to clean hard surfaces. The lotions are harsher on the skin and the web; therefore in order to protect the consumer, the wipes have been dispensed from canisters rather than from tubs. The canisters have a small aperture at the top through which the pre-moistened wipe must be drawn. Therefore, the webs must have a higher wet tensile than in the past to withstand the additional strain and must also be stable to the harsher lotions. The new wipes that are being introduced today for these applications use spunbond or melt-blown fabric instead of airlaid web. The spunbond or melt-blown webs are more expensive, non-biodegradable and less absorbent than airlaid webs. These drawbacks are the driving force for developing airlaid webs with the required strength.
Due in part to regulations in Europe, regarding use of alkylphenol ethoxylate (APE)-based products, there is also a need to use APE-free polymer emulsion binders in preparation of nonwoven webs for use in wet wipes.
Examples of known polymer emulsions binders for use in nonwovens are described below:
U.S. Pat. No. 5,180,772 (Mao et al., 1993) discloses vinyl acetate/ethylene copolymer emulsions having extended shelf and useful as binders for nonwovens. Nonwoven products formed by depositing the emulsion onto a nonwoven substrate exhibit improved resistance to organic solvents.
U.S. Pat. No. 5,540,987 (Mudge et al., 1996) discloses a low formaldehyde emulsion binder that is useful in improving the tensile properties of nonwovens.